The present invention relates to an actuator unit, particularly for actuating variable valve control systems, having an actuator and a deflection device that deflects the motion of the actuator to a substantially linear actuating motion.
Such actuator units are known in various embodiments in the prior art. For instance, it is known to embody the actuator as a hydraulic drive. The motion of the actuator is engendered in the hydraulic drive by increasing the pressure in the hydraulic medium. It is also known to provide an electric motor as the actuator, whose rotary motion is deflected to a linear actuating motion by means of a thrust rod worm gear.
These known actuator units are often used to actuate variable valve control systems in internal combustion engines, preferably to control a variable valve stroke.
The known actuator units have the disadvantage of low actuation dynamics. Because of the damping action of the hydraulic medium in an actuator embodied as a hydraulic drive or because of the inertia of the rotating masses to be accelerated in the case of an actuator embodied as an electric motor, the known actuator units have quite long actuation times.
It is accordingly an object of the present invention to design and refine the actuator units of the type defined at the outset in such a way that the actuation dynamics are increased.
To attain this object, the actuator unit of the type defined at the outset is embodied as an electromagnet.
The actuator units of the invention have very high actuation dynamics, because in comparison with the known actuator units, delays caused by the damping action of a hydraulic medium or the inertia of the rotating masses of an electric motor are virtually eliminated.
According to an advantageous refinement of the present invention, the deflection device has a lever element, supported rotatably about a first pivot point, with a connecting rod rotatably connected to the lever element about a second pivot point, and the lever element is articulated by means of the armature or the electromagnet, and the connecting rod upon actuation of the electromagnet executes the substantially linear actuating motion. By means of a deflection device designed in this way, the motion of the electromagnet can be converted into a linear actuating motion. This makes it possible to dispense with complicated, high-maintenance, vulnerable deflection gears. The deflection device according to this refinement operates with especially low loss.
Advantageously, for the rotatable connection about the second pivot point, a connecting rod eyelet is embodied on a first end of the connecting rod and is connected to a correspondingly embodied counterpart of the lever element. The counter part of the lever element can for instance be embodied as a peglike round piece, which is rotatably received by the connecting rod eyelet.
In a preferred embodiment of the actuator unit of the invention, the counterpart is rotatable about the second pivot point, thereby overcoming a static friction force in the connecting rod eyelet. The static friction force acts counter to the pulsating reaction forces from the valve drive of the variable valve control system to be actuated. As a result, virtually any arbitrary setting position of the actuator unit of the invention can be maintained when there is little or no current to the electromagnet. For actuating the variable valve control systems, this embodiment requires only little actuation energy. Furthermore, the static friction that occurs in the deflection device reduces coupling vibration exerted on the actuator unit by the valve control system to be actuated. A rigid embodiment of the connecting rod reinforces this action of reducing the coupling vibration as well, because as a result the free development of the pulsating reaction forces is effectively suppressed. Because of the provisions for reducing the coupling vibration in the actuator unit, the electromagnet is widely protected against disruptive or even damaging oscillation or vibration.
Advantageously, the ratio of the spacing between the first pivot point and the second pivot point to the radius of the connecting rod eyelet is less than the coefficient of adhesion xcexc0 between the material of the connecting rod eyelet and the material comprising the lever element. In this case, via the connecting rod, forces introduced into the actuator unit by the variable valve control system to be actuated are compensated for by the forces of static friction in the connecting rod eyelet in such a way that they do not engender any torque with respect to the first pivot point. In this way, it is possible to successfully keep pulsating reaction forces from the valve drive away from the armature of the electromagnet.
Preferably, the second pivot point between the counterpart and the connecting rod eyelet is disposed between the first pivot point of the lever element and the first articulation point of the armature on the lever element. The longitudinal axis of the lever element extends approximately perpendicular to the substantially linear motion of the armature of the electromagnet. The longitudinal axis of the connecting rod in turn extends approximately perpendicular to the longitudinal axis of the lever element. Thus, the longitudinal axis of the connecting rod extends approximately parallel to the substantially linear motion of the armature. The connecting rod and the armature of the electromagnet are articulated on the same side of the lever element. In this way, a linear motion of the armature of the electromagnet can be deflected to a substantially oppositely oriented linear actuating motion.
By positioning the second pivot point near the first pivot point, the force of the actuating motion can be increased while the force and stroke of the armature are constant, but the length of the actuating motion is shortened. Conversely, by positioning the second pivot point farther away from the first pivot point, the length of the actuating motion can be increased, but then the force of the actuating motion becomes less. By means of a suitable positioning of the second pivot point relative to the first pivot point, the actuator unit can be adapted to applicable conditions, and in particular to the technical characteristics of the valve control system to be actuated.
In an advantageous alternative embodiment, the first pivot point of the lever element is disposed between the second pivot point between the counterpart of the connecting rod eyelet and the first articulation point of the armature on the lever element. In this embodiment, the direction of motion of the armature is deflected to an oppositely oriented actuating motion.
In another preferred embodiment, an intermediate element is disposed between the armature and the lever element. By means of this intermediate element, a deviation from a linear motion on the part of the lever element can be compensated for if the lever element is rotated about the first pivot point by the linear motion of the armature. That is, because of the rotary motion of the lever element about the first pivot point, a relative motion of the first articulation point of the lever element also occurs perpendicular to the linear motion of the armature in the direction of the first pivot point.
Advantageously, the second end of the connecting rod articulates a coupling lever of a variable valve stroke (VVH) system to a first end of the coupling lever, and the coupling lever is rotatably supported on a second end about a third pivot point. The advantages of the actuator unit of the invention are especially valuable when the actuator unit is used in VVH systems.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing.